Gal Oya National Park in Sri Lanka was established in 1954 and serves as the main catchment area for Senanayake Samudraya, the largest reservoir in Sri Lanka. Senanayake Samudraya was built under the Gal Oya development project by damming the Gal Oya at Inginiyagala in 1950. An important feature of the Gal Oya National Park is its elephant herd that can be seen throughout the year. Three important herbs of the Ayurveda medicine, Triphala: Aralu, Bulu and Nelli are amongst the notable flora of the forest.

From 1954 to 1965 the park was administrated by the Gal Oya Development Board until the Department of Wildlife Conservation took over administration. The National Park is situated 314 km from Colombo
The Gal Oya Development Board established several protected areas to protect the catchment areas of Senanayake Samudraya and several other reservoirs. This also helped to prevent the soil erosion caused by burning of the Thalawa grassland by the villagers. The protected areas established in 1954 are Gal Oya National Park, Senanayake Samudraya Sanctuary, Gal Oya valley north-east Sanctuary, and Gal Oya valley south-east Sanctuary.

Together these four reserves accounts for 63,000 hectares of land. Administration and protection of the four protected areas, reducing human-elephant clashes and enforcing the flora and fauna ordinance are amongst the duties of the department. Rangers are stationed in four sites: Inginiyagala, Mullegama, Nilgala and Baduluwela. Additionally in 1974 the Buddangala Sanctuary was also designated. Buddangala is a monastery with ruins of a Stupa and other buildings in the nearby Malwatta area.

The vegetation of the forest is of three types; forests, shrubs and grasslands. The national park contains a substantial area of Savannah grasslands known as Thalawa in Sinhalese and mountainous grasslands known as Pathana. Thalawa grassland is dominated by rough grass species, Mana and Iluk. The burnt Thalawa grasslands are known as the Damana grasslands and are used for cattle grazing by villagers. Rare plants of medicinal value are also found in the forest.

Thirty two terrestrial mammals have been recorded in the park. The Sri Lankan Elephant, Sri Lankan Axis Deer, Muntjac, Water Buffalo, Sri Lankan Sambar Deer, Sri Lanka Leopard, Toque Monkey and Wild Boar are among them. Included amongst the amphibian species of the park are the Mugger Crocodile and Star Tortoise. More than 150 species of birds have been recorded in Gal Oya. The Lesser Adjutant, Spot-billed Pelican and Red-faced Malkoha are some of the park's resident birds. The Indian Cormorant, Oriental Darter, Grey Heron, and Lesser Whistling Duck are among the common water birds of the Senanayake reservoir. White-bellied Sea Eagle and the Grey-headed Fish Eagle are the notable raptors of the area. Gal Oya National Park's butterfly species include the endemic Lesser Albatross.